1. Field of the Invention
This invention relates to a liquid injection recording apparatus, and more particularly to a liquid injection recording apparatus which can accomplish harmonious recording.
2. Description of the Prior Art
Non-impact recording methods have recently been attracting attention in that noise occurring during recording is negligible. Among them, the so-called ink jet recording method (or liquid injection recording method) which is capable of effecting high-speed recording without requiring special processing such as fixation on plain paper is a very effective recording method, and heretofore various types of such method have been proposed and apparatuses embodying them have been to devises some of which have already been commercialized and some of which are still being studied in order that they may be put into practical use.
Among them, the liquid injection recording methods disclosed, for example, in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Patent Application (DOLS) No. 2843064 have a feature different from other liquid injection recording methods in that heat energy is caused to act on liquid to thereby obtain a generative power for discharging drops of liquid.
That is, in the recording methods disclosed in the aforementioned publications, the liquid acted on by the heat energy undergoes a state change involving a sharp increase in volume and, by the force resulting from such state change, drops of liquid are discharged and fly from an orifice provided at the tip end of the recording head portion and adhere to a recording medium, thus accomplishing recording.
Particularly, the liquid injection recording method disclosed in DOLS No. 2843064 can not only be very effectively applied to the so-called drop-on demand recording method, but also has an advantage that it readily permits the provision of high-density multiorifice recording heads across a full line width, and therefore images of high resolution and high quality can be obtained at a high speed.
Thus, the above-mentioned liquid injection recording method has various advantages, but when it is desired to record images of higher resolution and higher quality, it is necessary to endow recorded picture elements with harmony and effect image recording including half-tone information.
As a first one of such image recording methods having tone controllability, there is a recording method in which a picture element is divided into a matrix-like form in a plurality of cells each of which can be occupied only by one of image forming element and harmony of a desired level is digitally expressed in conformity with the number of cells occupied by the image forming elements, of those cells made into the matrix-like form, and the arrangement condition of the image forming elements which occupy the cells. As a second method, there is a recording method in which a picture element is constituted by only one image forming elements and a desired expression of harmony is effected analogously by changing the optical density of the image forming element.
However, in an ink jet recording head which effects recording with liquid caused to be discharged by heat energy, if the first tone control method is resorted to, the area of one picture element itself will become great and this is liable to result in a reduction in sharpness, etc. Also, the fact that this method uses digital control makes the tone steps rough, and this has led to a problem that the quality of image lacks delicacy. The second tone control method is generally a method of varying electrical energy for increasing the size of drops of liquid discharged and thereby varying the size of a picture element, namely, an image forming element. This method, however, has suffered from the problems that the control range of harmony is narrow and a sufficient tone control range cannot be obtained and that there occurs unsatisfactory discharging of the recording head and reduced reliability of the head.